The present invention is generally related to a pressure activated isolation valve for use in anti-lock/traction control braking systems.
In many instances it is considered desirable to isolate the brake pedal from the operation of the anti-lock and/or traction control system. This isolation is desirable so that these systems do not interfere with normal brake pedal operation. As an example it is undesirable for an anti lock system to feed back to the brake pedal to cause it to move from the position established by the operator. Similarly it is undesirable for a traction control system to activate the brakes of the non-driven wheels. As such, it is desirable to incorporate into such systems an isolation valve. Prior systems have suggested using solenoid valves to isolate the anti lock system from the brake pedal and/or from the master cylinder. Without such isolation the vehicle operator may become distracted at inopportune moments due to unexpected movement of the brake pedal. However, the inclusion of the solenoid valves and associated wiring to accomplish the isolation function increases cost, and may lower the overall reliability of the system.
It is a purpose of the present invention to provide means which obviates the need for solenoid valves to achieve the desired isolation of the master cylinder from the remainder of the anti-lock/traction braking system. Another purpose of the present invention is to provide an anti-lock/traction braking system which uses pressure activated isolation valves. A further purpose of the present invention is to provide means for automatically preventing the operation of the isolation valve(s) if adequate pressure is not available for reapplication of brake force (after release) during anti-lock system operation. An additional purpose of the present invention is to utilize many of components of an anti-lock system to control tractive effort. Accordingly the invention comprises: a pressure responsive isolation valve for use within an adaptive braking system comprising: passage means including a first port adapted to receive pressurized fluid from a first pressure source, an outlet port adapted to communicate with various brake cylinders, a second port adapted to communicate fluid to or from control valves; and a pressure port remote from the other ports, adapted to receive pressured fluid from a second pressurized source. The isolation valve further includes: valve means movable to open and close one or another of opposingly situated passages and to alternatively communicate the first port to the outlet port or the second port to the outlet port; means for moving the valve means relative to the passages, including first means movable in response to pressurized fluid from the second source for urging the valve means to seat upon the first passage to control communication to and from the first source to the output port.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.